Actuator for chemical injector or the like



March 15, 1955 MQFARLAND 2,704,053

ACTUATOR FOR CHEMICAL INJECTOR OR THE LIKE Filed Nov. 25, 1949 s Shee ts-Sheet 1 57 Ar zhur E. M Far/ona 6 IN VEN TOR.

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Mar ch 15, 1955 A. E. MCFARLAND ACTUATOR FOR CHEMICAL INJECTOR OR THE LIKE Filed Nov 25, 1949 3 Sheets-Sheet 2 A r fhur- E. M For/anc INVENTOR.

A TTORA/EKS March 15, 1955 A. E. M FARLAND ACTUATOR FOR CHEMICAL INJECTOR OR THE LIKE Filed Nov. 25, 1949 5 Sheets-Sheet 3 Ar Zhur E. M for/00a INVENTOR.

A 770/?NEY5 United States Patent ACTUATOR FOR CHEMICAL INJECTOR OR THE LHCLE Arthur E. McFarland, Houston, Tex., assignor to McFarland Manufacturing Corporation, Houston, Tex., a corporation of Texas Application November 25, 1949, Serial No. 129,235

12 Claims. (Cl. 121-150) This invention relates to improvements in reciprocating type actuators and refers more particularly to an actuator of this class powered by pressure fluid and especially adapted for use with chemical injectors.

This application covers an invention which is an improvement upon the invention disclosed in my co-pending application filed December 21, 1948, assigned Serial Number 66,435 of the Series of 1948, for a Pump and Motor Therefor, now issued as United States Letters Patent Number 2,594,577.

While the actuator of this invention has many uses for which it is adapted, the use that applicant is primarily concerned with is as a motor for a chemical injector for forcing emulsion breaking chemicals into crude petroleum produced from the ground. Accordingly, by way of example and not by way of limitation, this specification will be restricted to a large degree to disgufgiol'l of this invention as applied in this particular In producing crudepetroleum from the earth, it is frequently desirable to break down emulsions which occur with the production of petroleum from wells so that the well fluids can be separated into a gas, a petroleum liquid, and water or salt water. One commercially practiced method for breaking down these emulsions involves the injection of certain chemicals into the well fluids. The ratio of chemical to well fluids, required to effectively and economically do this, can be determined with considerable degree of accuracy by those skilled in the art, but it has heretofore presented quite a problem as to how to inject these chemicals into the fluid in the precise ratio required. Obviously, the elfect of these chemicals is dependent to a considerable extent upon their uniform distribution throughout the well fluids. It is frequently necessary to continuously inject the chemicals into fluids over prolonged time periods and therefore an actuator having a minimum number of moving parts is desirable in the interest of prolonging the life of the actuator. Also, the well fluids are produced throughout the entire year and it is desirable that weather and temperature changes do not affect the frequency or length of stroke of the actuator in order that a constant amount of chemical may be injected into the well fluids. It is also desirable that the equipment be capable of operation at a high frequency but that the amount of chemical pumped with each stroke be small and controllable to aid in proper distribution of the chemical.

An object of this invention is to provide an actuator of the type described having very few moving parts.

Another object is to provide an actuator of the type described which will maintain the same frequency and length of stroke regardless of weather and temperature changes.

A further object is to provide a device of the character described which may operate at a selected frequency over a large range but which will pump a small uniform quantity of chemical upon each stroke.

Still another object is to provide an actuator of the type described which operates very smoothly and quietly.

A still further object is to provide an actuator of the type described in which the return portion of the stroke of the reciprocating member allows sufficient time to insure an intake of chemical even though the chemical is very viscous.

Other and further objects of the invention will appear as this description proceeds.

in the accompanying drawings forming a part of the instant specification to be read in conjunction therewith and wherein like reference numerals are employed to indicate like parts in the various views:

Fig. 1 is an isometric view illustrating an actuator embodying this invention;

Fig. 2 is a vertical section, upon an enlarged scale, of the device shown in Fig. 1, with certain of the connections for both the actuator housing and slide valve means shown in dotted lines at approximately to their true positions to illustrate their relative position along the axes of these members respectively;

Fig. 3 is a horizontal sectional view taken along the line 33 in Fig. 2 in the direction of the arrows;

Fig. 4 is a view taken along the line 4-4 in Fig. 2 in the direction of the arrows and illustrates some of the ports shown in Fig. 2 in dotted lines to show their relative positions along the longitudinal axis of the casing of the slide valve; and

Fig. 5 is a view similar to Fig. 2 but shows the pressure responsive members and the slide valve means in their other extreme and operative positions respectively as compared to the Fig. 2 showing.

Referring to Fig. 1, it will be seen that the apparatus comprises three main components, namely, the power cylinder 6, a slide valve means 7 for controlling flow of pressure fluid and exhaust to and from the apparatus 6 and a pressure regulator 8 supplying a source of pressure fluid under constant pressure.

Referring to Fig. 2, the apparatus 6 will be seen to comprise a power cylinder or housing 9 having an internal bore of three different diameters 10, 11 and 12. The portions provided by bores 10 and 12 provide chambers or power cylinders of different diameters. The intermediate section provided by bore 11 provides a reservoir for a lubricant if this is desired.

The interior of cylinder 9 is provided with two pressure responsive members, one residing within each of the power chambers. These pressure responsive members may be in the form of pistons 13 and 14. The effective area of the piston 13 and its chamber and the piston 14 and its chamber will be seen to be considerably ditferent so that when both chambers are pressurized, the pressure responsive members will be moved to the left as viewed in Fig. 2. However, when the pressure to the right of piston 14 is vented and the chamber to the left of chamber 10 is energized, the pressure responsive members will be forced to the right all as viewed in Fig. 2.

A force transmitting connection is provided between the two pistons by rod 15 which may be threaded at its ends to the two pistons with lock washers 16 and 17 securing the pistons in place.

To utilize the power developed by the pressure responsive members within housing 9, one of the pressure responsive members may be connected to a member to be driven. In the embodiment shown, the member 13 is threaded to the driven rod 18 which extends from the left end of cylinder 9 through a suitable stufiing box assembly as shown. The rod 18 may be housed in a suitable casing 20 and may be connected to any apparatus to be driven and when the apparatus is a pump for injecting chemicals under pressure, the plunger 19 may be connected directly to the rod 18. In the interest of simplicity, the details of the pump have been eliminated from the drawings but they may be of the character shown in the above mentioned co-pending application. By varying the effective size of plunger 19 of a pump, the pressure at which fluid may be ejected from the pump may be varied, for a given pressure of operating fluid for the actuator.

The pistons 13 and 15 preferably have traveling seals with their respective cylinders. The seal on piston 13 may be V-type packing elements 21, retaining rings 22 triangular in cross-section, and a washer 23 held in position by lock nut 24, to hold the retainer ring 22 in position as shown in Fig. 2. A suitable seal arrangement is shown for piston 14 in the form of an O-ring 25 residing within a groove formed in the periphery of the piston.

The right end of cylinder 9, as viewed in Fig. 2, is closed with a cover plate 26 threaded thereto and preferably an O-ring 27 is provided in a groove in the cap to seal the joint. A drain plug 29 may be provided for draining lubricant from the interior of the central chamber of cylinder 9, and this chamber is vented through an opening 30 in its upper end which may be fitted with a vent fitting 31 as a tube threaded in opening 30 and having a vented cap 32 at its upper end, as shown in Fig. 1.

Power fluid, under pressure, is introduced into the chamber provided by bore 10, through port or inlet 33 which communicates through a fitting 34 with a source of constant pressure. This source of constant pressure preferably is the regulator 8 which may be of any conventional make, and the operating pressure put out by the regulator may vary from 15 p. s. i. to 120 p. s. i. The regulator has a fitting 35 which communicates with some suitable source of fluid under pressure.

The chamber provided by bore 10 has another port 36 which is located so as to communicate with the chamber on the power side of piston 13 when the piston is in its extreme right position as shown in Fig. 2, but which communicates with the interior of the chamber provided by bore 11 and consequently with atmosphere due to the vent cap 32, when the piston has traveled sufliciently to the left as viewed in Fig. 2 for the seal rings 21 to have traveled over the port 36. In order to minimize the wear upon the seal rings due to their passing over the openings 36, it is desirable to keep the port 36 very small and a plurality of small converging ports may be employed, all aligned in a plane normal to the longitudinal axis of the cylinder 9 if it is necessary to increase the orifice capacity. The port 36 and the fitting 37 with which it communicates is provided for the purpose of supplying pressure to and venting pressure from one side of a pressure responsive element in a slide valve mechanism, in a manner hereinafter more fully described.

Power fluid is introduced into the main chamber provided by bore 12 through an opening 38 in cover plate 26. Also, power fluid may be vented through this same opening after it has been spent and upon the return stroke of piston 14. The manner in which this pressure fluid is supplied to and vented from the chamber provided by bore 12 will be hereinafter more fully explained in connection with the slide valve mechanism 7. This chamber has a port 39 which also leads to this slide valve mechanism 7 to contribute to its actuation. This port 39 is positioned so as to be exposed to the chamber of cylinder 9 intermediate pistons 13 and 14 when the piston is in a position so that the O-ring 25 is to the right of the port, when the device is viewed as in Fig. 2. On the other hand, when the piston is in such position that the O-ring 25 is moved to the left of port 39, then the port is exposed to the interior of the power chamber for actuating piston 14. This latter position will be more readily shown by reference to Fig. 5.

Referring now to the slide means, it will be seen to comprise a casing or housing made up of a tubular part 40 having end caps 41 and 42 sealing the ends thereof and secured in place by threads. The O-ring seals shown in the drawings for this purpose are satisfactory but other seal means may be employed. Within the housing there is provided an actuation chamber 43 and a valve chamber 44. The valve chamber has communication with a source of power fluid through fitting 45 and communicates with the vent fitting 31 through conduit 46. An intermediate port 47 communicates with port 38 through pipe segment 48, union 49, needle valve 50 and pipe segment 51. The needle valve is not shown in detail because it constitutes conventional well known equipment but provides a means for varying the capacity of the flow line provided by parts 48, 49, 50 and 51. Its purpose is to provide a means for regulating the speed or frequency of the actuator.

Referring back to valve chamber 44, it will be seen that seats 52 and 53 have been provided intermediate fittings 45 and 46. It will also be seen that the port 47 is intermediate these two seats. Avalve member 54 is operably mounted within the chamber 44 to control flow therethrough by seating against seats 52 and 53. With the valve member seated against seat 52, power will be supplied from the regulator through fitting 45 and the chamber 44 into pipe 48 and thence into the main power chamber of the actuator. On the other hand, when the valve element 54 is in its right hand position, as viewed in Fig. 2, seated against seat 53, the interior of the main power cylinder, of the actuator will communicate with the vent connection 46. By using a single fitting and needle 50 for regulating flow of both the power and exhaust fluids to and from the main power chamber of the actuator, there is little opportunity for debris or other material to clog up the needle valve because the constant geilljersal of direction of flow of fluid will dislodge any e ris.

The valve member 54 is carried upon a rod 55 which extends in both directions from the valve member. The right hand end of rod 55, as viewed in Fig. 2, carries a plug 56 which reciprocates in a bore through cap 42. An O-ring 57, which may be located in a groove formed in cap 42, provides a sliding seal between the cap and the rod 56. The effective pressure area of plug 56 preferably is substantially the same as the area across seat 53 so that with the valve member 54 seated at 53, the force due to the pressure from fitting 45 acting against the plug will substantially counter-balance the force due to this pressure acting against the valve member 54. On the other hand, the area of seat 52 should be greater than the area across plug 56 so that with the valve member 54 seated at 52, the force of the power fluid acting against the valve member will be greater than force of the power fluid acting against the plug so that the valve member will positively seat and prevent escape of power fluid through the vent 46.

The left end of rod 55, as viewed in Fig. 2, carries a piston 58, which has a seal means as O-ring 59 carried in a peripheral groove, providing a sliding seal between the piston and the wall of the housing 40 which provides the chamber 43. The piston has a sleeve like extension 60, of considerably reduced diameter, which fits over a reduced diameter threaded portion on the left end of rod 55 and abuts a shoulder at the end of the reduced diameter portion. Nut 63 holds the piston in place. The sleeve 60 has an enlarged diameter portion 61 which carries a seal means, as O-ring 62a, providing a sliding seal with bore 400 in the valve housing. The reduced diameter portion of sleeve 60 provides an annulus establishing communication between a port 62 and the main portion of the actuating chamber 43 on the right hand side of piston 58, as viewed in Fig. 2. This port 62 is shown in dotted lines at about from its actual position circumferentially of the casing, in order to show its relative position along the axis of the slide valve casing. It will be noted by reference to Figs. 2 and 5 that this port always communicates with the actuating chamber 43, for the purpose of supplying power fluid to the chamber and exhausting spent fluid from the chamber in a manner to be hereinafter more fully explained.

A fitting 64 is secured in a central opening in cover plate 41 and is adapted to supply power fluid to the actuating chamber on the left hand side of piston 58, as viewed in Fig. 2, and to exhaust spent power fluid therefrom in a manner to be next described.

In order to actuate the slide valve so as to properly control the supply of power fluid to the main piston 14 of the actuator and to properly exhaust spent fluid therefrom, a means is provided for actuating piston 58 in both directions in response to the position of the main piston 14 and piston 13 of the actuator. To accomplish this, the port 62 may be connected by connection 37 to the port 36 in the cylindrical portion 10 of the actuator. It will be appreciated that with this arrangement the right hand side of pston 58 will be exposed to power fluid when the piston 13 is in its Fig. 2 position but that when the piston 13 moves to the left, as shown in Fig. 5, sufficiently for the seal means 21 to have passed over the ports 36, that the right hand side of piston 58 of the slide valve actuator will be vented.

Power fluid may be supplied to and vented from the other side of piston 58 by connecting fitting 64 with port 39 so that power fluid is supplied to chamber 43 on the left hand side as viewed in Fig. 2, when the main piston 14 is in its Fig. 5 position. When main piston 14 travels toward its Fig. 2 position sufliciently for the seal means 25 to have passed over the port 39, this portion of chamber 43 will be vented. During travel of pistons 13 and 14 between their extreme positions, the pressure acting against the valve element 54 holds it on its seat.

These connections may all be seen in the isometric drawing of Fig. 1 where it will also be seen that, connected to regulator 8, is a fitting 34 which supplies a constant source of power fluid to the chamber within bore of the actuator. The fitting 45 which connects with the regulator is adapted to supply power fluid intermittently to the piston 14, this supply of power fluid being controlled by the slide valve.

In operation, the cylindrical bore 10, on the left hand side of piston 13, as viewed in Fig. 2, is always pressurized with a constant pressure from the regulator. This pressure acts against an effective pressure face substantially equal to the annular area of piston 13 exterior of rod 18 serving as a means for yieldably urging the piston to the right. When the same pressure is exposed to the face of piston 14 on the right hand side of the piston as viewed in Fig. 2, this pressure, acting against a greater area, will move the piston 14 to the left. On the other hand, when this right hand face of piston 14 is exposed to atmospheric pressure, or some vented pressure, then the force due to the pressure fluid acting against piston 13 will drive the main piston to its Fig. 2 position.

This intermittent supply of power fluid to piston 14, with alternate venting of the piston, is accomplished by the slide valve mechanism which in turn is operated by the actuator including the piston 58 and the connections 37 and 64 which supply power fluid to and exhaust spent power fluid from chamber 43 on both sides of piston 58 in response to the positions of main piston 14 and piston 13 of the actuator.

Considering the mechanism in its Fig. 2 position, the main piston 14 has just been driven to its extreme right position and it then is necessary that the right hand side of piston 14 be energized by supplying pressure fluid thereto. This happens substantially simultaneously with ports 36 being exposed to the pressure within cylinder 10 of the actuator, for the port 39 at this time is in communication with vent 31. The pressure fluid is thus supplied to the actuating chamber 43 on the right hand side of piston 58 to drivethe piston into the position as shown in Fig. 2. The'piston prior to that, of course, was in the position shown in Fig. 5.

Under the influence of the actuator including piston 58, the valve element 54 is shifted from its Fig. 5 position against seat 53 to its seated position against seat 52. Pressure fluid is then supplied from the regulator through line 45 through the annulus surrounding the right hand end of rod 55 and thence through port 47, fitting 48, union 49, needle valve 50 and connection 51 to the interior of chamber 12 of the actuator on the right hand side of piston 14 as the actuator is viewed in the figures of the drawings.

Immediately upon pistons 13 and 14 reaching their Fig. 5 positions, connection 64 is energized with the power fluid within chamber 12 on the right hand side of piston 14 because the port 39 is upon the right hand side of seal means 25. Prior to this the connection 37, between port 36 and port 62, has vented the actuating chamber 43 on the right hand side of piston 58, so that upon energization of chamber 43 on the left side of piston 58, the piston is driven sharply to the right to its Fig. 5 position to seat the valve 54 at 53.

With the valve element 54 seated at 53, chamber 12, on the right hand side of piston 14, is vented through the fitting containing needle valve 50, through the slide valve mechanism and connection 46 leading to vent 31.

With this arrangement of the parts, the pressure within bore 10, to the left of piston 13, drives piston 13 and the main piston 14 to their Fig. 2 positions.

The needle valve 50 can be adjusted in a manner well known to those skilled in the art by rotating pin 70 to vary the size of the opening for supplying pressure and venting spent fluid to and from port 38. By changing the size of the orifice, past the needle valve, the frequency of the actuator may be varied from a very high frequency to an extremely low frequency. Inasmuch as pressure fluid and exhaust fluid are constantly passing past the needle valve in opposite directions, it has been found that there is very little tendency for debris to clog this fitting.

cant are carried to the slide valve housing to lubricate its moving parts.

From the foregoing it will be seen that this invention provides an actuator which is especially adapted for reciprocally driving a driven member such as plunger 19 for a chemical injector. The driving of member 19 is independent of any temperature change so that the length of stroke and the speed of the stroke is not affected by temperature changes. The construction is such that the actuator operates very smoothly and positively at both high and low frequencies and involves only a minimum number of moving parts which may be lubricated to prolong the life of the instrument. The arrangement is such that the actuator may be operated at very high frequency and still pump only small portions of the chemical to be pumped on each stroke. The device of this invention is such that it will operate continuously without attention over prolonged periods of time.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention Without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1. A reciprocating type actuator comprising a housing having two spaced power chambers of different effective areas, pressure responsive members operably mounted for reciprocating in each chamber, each of said members having a pressure responsive side, pressure fluid inlets for admitting fluid under pressure into each chamber upon the pressure responsive sides of the pressure responsive members to urge them in opposite directions, a power transmitting connection between the pressure responsive members, one of said pressure responsive members adapted to have a power transmitting connection with a member to be driven, and slide valve means controlling the inlet for power fluid for only the chamber of largest effective area, said means being responsive to fluid under pressure from said chambers to establish communication between the chamber of largest effective area and a source of power fluid when the pressure responsive member therein is in position to commence its power stroke and to vent said latter chamber when the pressure responsive member therein is in its other extreme position.

2. The arrangement of claim 1 wherein the housing between the power chambers has a vented chamber providing a lubricant receiving space between the pressure responsive members.

3. A reciprocating type actuator comprising a housing having two spaced power chambers of different effective areas, pressure responsive members operably mounted for reciprocation in each chamber, a each of said members having a pressure responsive side, pressure fluid inlets for admitting fluid under pressure into each chamber upon the pressure responsive sides of the pressure responsive members to urge them in opposite directions, a power transmitting connection between the pressure responsive members, slide valve means for alternately establishing communication between the chamber of larger effective area and a source of power fluid and a vent, a fluid driven actuator for the slide valve means for alternately shifting it between its effective positions, and connection means between the power chambers and the fluid driven actuator providing power fluid for the fluid driven actuator from each chamber When the pressure responsive member in each power chamber is in position within its chamber at the end of its power stroke.

4. A reciprocating type actuator comprising a housing having two spaced power chambers of different effective areas, pressure responsive members operably mounted for reciprocation in each chamber, each of said members having a pressure responsive side, pressure fluid inlets for admitting fluid under pressure into each chamber upon the pressure responsive sides of the pressure responsive members to urge them in opposite directions, a power transmitting connection between the pressure responsive members, slide valve means for alternately establishing communication between the chamber of larger effective area and a source of power fluid and a vent, a fluid driven actuator for the slide valve means for alternately shifting it between its effective positions, and connection means between the power chambers and the fluid driven actuator providing power fluid for the fluid driven actuator from each chamber when the pressure responsive member in each power chamber is in position within its chamber at the end of its power stroke, said slide valve means having a power connection and vent connection with an intermediate connection with the inlet of the power chamber of larger area, a valve seat between the intermediate connection and each of the other connections, and a valve member connected to the fluid driven actuator to be shifted thereby to seat against said seats.

5. A reciprocating type actuator comprising a housing having two spaced power chambers of different effective areas, pressure responsive members operably mounted for reciprocation in each chamber, each of said members having a pressure responsive side, pressure fluid inlets for admitting fluid under pressure into each chamber upon the pressure responsive sides of the pressure responsive members to urge them in opposite directions, a power transmitting connection bctween the pressure responsive members, slide valve means for alternately establishing communication between the chamber of larger effective area and a source of power fluid and a vent, a fluid driven actuator for the slide valve means for alternately shifting it between its effective positions, and connection means between the power chambers and the fluid driven actuator providing power fluid for the fluid driven actuator from 30 each chamber when the pressure responsivemember in each power chamber is in position within its chamber at the end of its power stroke, said valve means having a single valve member operably connected to the fluid driven actuator for alternately establishing communication between the inlet of the larger area power chamber and a power source and a vent.

6. A reciprocating type actuator comprising a housing having two spaced power chambers of different effective areas, pressure responsive members operably mounted for reciprocation in each chamber, each of said members having a pressure responsive side, pressure fluid inlets for admitting fluid under pressure into each chamber upon the pressure responsive sides of the pressure responsive member to urge them in opposite directions, a power transmitting connection between the pressure responsive members, slide valve means for alternately establishing communication between the chamber of larger effective area and a source of power fluid and a vent, a fluid driven actuator for the slide valve means for alternately shifting it between its effective positions, and connection means between the power chambers and the fluid driven actuator providing power fluid for the fluid driven actuator from each chamber when the pressure responsive member in each power chamber is in position at the end of its power stroke, said valve means having a single valve member operably connected to the fluid driven actuator for alternately establishing communication between the inlet of the larger area power chamber and a power fluid source and a vent, the pressure of the power fluid holding the valve member in pressure supply position with a force less than that which the fluid driven actuator is capable of imposing upon it when energized to shift the valve member to the other position.

7. The arrangement of claim 6 wherein an adjustable constriction is disposed in the connection of the inlet of the larger area power chamber with both the power source and the vent whereby the construction is kept open by the fluid flowing in alternate directions.

8. A reciprocating type actuator comprising a housing with two chambers, two differential area pressure responsive members, each of said members having a pressure responsive side, one in each chamber, power transmitting means between the pressure responsive members, connection means for supplying pressure fluid to each chamber on the pressure responsive sides of the pressure responsive members to drive them in opposing directions, valve means controlling the connection means for the pressure responsive member of larger area adapted to selectively energize and vent only the latter chamber, fluid driven actuator means controlling the valve means to alternately energize and vent the latter chamber, and means to supply power fluid to the actuator means from the chambers when the pressure responsive members therein reach the end of their power strokes respectively.

9. A reciprocating type actuator comprising a housing having spaced power chambers of different effective areas, pressure responsive members operably mounted for reciprocation in each chamber, each of said members having a pressure responsive side, pressure fluid inlets for admitting fluid under pressure into each chamber upon only the pressure responsive sides of the pressure responsive members to urge them in opposite directions, a power transmitting connection between the pressure responsive members, one of said pressure responsive members adapted to have a power transmitting connection with a member to be driven, valve means controlling the inlet for power fluid for the chamber of largest effective area, communicating means between said valve means and each of said chambers and entering said chambers at points other than said pressure fluid inlets, said valve means being responsive to fluid under pressure from said chambers and through said communicating means to establish communication between the chamber of largest effective area and a source of power fluid when the pressure responsive member therein is in position to commence its power stroke and to vent said latter chamber when the pressure responsive member therein is in its other extreme position.

10. An actuator of the character defined in claim 9, the entrance of each communicating means into its respective chamber .being located at opposite sides of the pressure responsive member for said chamber when said member is moved from one limit of reciprocation to the other.

11. A reciprocating type actuator comprising a housing having spaced power chambers of different effective areas,

pressure responsive members operably mounted for reciptransmitting connection between the pressure responsive members, one of said pressure responsive members adapted to have a power transmitting connection with a member to be driven, valve means controlling the inlet for power fluid for the chamber of largest effective area, actuating means for said valve means, communicating means between said actuating means and each of said chambers and entering said chambers at points other than said pressure fluid inlets, said actuating means being responsive to fluid under pressure from said chambers and through said communicating means for causing said valve means to establish communication between the chamber of largest effective area and a source of power fluid when the pressure responsive member therein is in position to commence its power stroke and to vent said latter chamber when the pressure responsive member therein is in its other extreme position.

12. An actuator of the character defined in claim 11, the entrance of each communicating means into its respective chamber being located at opposite sides of the pressure responsive member for said chamber when said member is moved from one limit of reciprocation to the other.

References Cited in the file of this patent UNITED STATES PATENTS 412,327 Gibson Oct. 8, 1889 1,123,678 Burlingham Jan. 5, 1915 1,306,301 Chadwick June 10, 1919 1,480,937 Gottschalk Jan. 15, 1924 1,521,628 Jones Jan. 6, 1925 1,540,962 Stuart June 9, 1925 1,865,913 Hynes July 5, 1932 2,090,583 Morton Aug. 17, 1937 2,389,621 Grise Nov. 27, 1945 FOREIGN PATENTS 394,147 Great Britain June 22, 1933 527,379 Great Britain Oct. 8, 1940 

